Humans are able to function in very dim light (e.g., moon light) and in intensely bright lights (e.g., the noon sun). To so this, the visual system must be able to adapt to a range of ambient light levels which varys by a factor of at least 108. This ability is called light adaptation. The research proposed here will expand on the knowledge of light adaptation, particular the temporal dynamics of light adaptation, through a series of experiments and modeling of the experimental results. The experiments will utilize stimuli from the probe-sinewave paradigm, a paradigm that has not been adequately studied. In a probe-sinewave experiment, a human observer's threshold is measured for detecting a small light (probe) surrounded by a flickering background. In the proposed experiments, various aspects of the stimulus will be manipulated (for example: the frequency, mean intensity, and amplitude of the flickering background; whether the probe is an increment or decrement in intensity with respect to the intensity of the background; the length of the flickering background before and after the probe; whether the probe and background are both presented to the same eye, or the probe is presented to one eye and the background to the other). Results from probe-sinewave experiments provide strong tests of light-adaptation models. There are two models we will concentrate our efforts on: Hugh Wilson's model (Wilson, 1997) and the merged-models of Graham and Hood (1992).